Preparation of alpha, omega-glycol esters



United States Patent PREPARATION OF ALPHA, ONIEGA-GLYCOL ESTERS SeaverA. Ballard and Richard R. Whetstone, Orinda, Califi, assignors to ShellDevelopment Company, Emeryville, Califl, a corporation of Delaware NoDrawing. Application October 1, 1953, Serial No. 383,685

Claims. (Cl. 260-491) This invention relates to a method of preparingdiesters of alpha,omega-dihydroxyalkanes containing at least four carbonatoms. More particularly, the present invention relates to a preferredaspect to a method for the preparation of aliphatic carboxylic aciddiesters of alpha,omegadihydroxyalkanes, i. e., of alkylene glycols,containing at least four carbon atoms. In another preferred aspect theinvention pertains to a method of preparing aromatic esters ofalpha,omega-dihydroxyalkanes containing at least four carbon atoms. Inspecific aspects the invention pertains to a method for the preparationof aliphatic carboxylic acid esters of hexamethylene glycol and, in afurther specific aspect, to a method for the preparation of diesters ofdialkyl-substituted 1,5-pentanediols.

Included in the process of the invention as its essential step is amethod for the preparation of diesters of alpha,- omega-dihydroxyalkenescontaining at least four carbon atoms, which unsamrated diesters may, ifdesired, be separated as useful products of the process, but which moredesirably are hydrogenated to form the above esters of the correspondingalpha,omega-dihydroxyalkanes.

Broadly stated, the invention comprises subjecting to pyrolysis atriester of an alpha,beta,omega-trihydroxyalkane containing at leastfour carbon atoms, to form as the principal products of the pyrolysistreatment diesters of alpha,omega-dihydroxyalkenes containing the samenumber of carbon atoms, which diesters may be hydrogenated to form inexcellent overall yield diesters of thedesiredalpha,omega-dihydroxyalkane. The diesters of thealpha,omega-dihydroxyalkanes readily may be converted to the freeglycols by methods that either are specifically known or will beapparent to those skilled in the art to which the invention pertains.

It has been proposed to prepare certain esters of unsaturated monohydricalcohols, e. g., of allyl alcohol and of the theoretical vinyl alcohol,by pyrolysis of diesters of alkylene glycols and by pyrolysis ofmonoesters of alkylene glycols. In both cases esters of dihydricalcohols are employed as the initial reactants, whereas we desire toproduce esters of dihydric alcohols. It also is known that glycerides,such as fats, and lower glycerides, such as triacetin, may be pyrolyzedto form acrolein and, in some cases, ketene. Both of these productsobviously are distinctly different from the products that are producedin accordance with the present invention.

It unexpectedly has been discovered in accordancewith the invention-thatcarboxylic acid triesters of alpha,beta,- omega-trihydroxyalkanescontaining at least four carbon atoms may be pyrolyzed to form as theprincipal products of the pyrolysis carboxylic acid diesters ofalpha,omegadihydroxyalkenes, in excellent yields and with a minimum offormation of undesirable by-products. It unexpectedly has beendiscovered further that the pyrolysis may be effected with a minimum ofaccompanying formation of esters of beta,omegaand/ oralpha,beta-dihydroxyalkenes, or products of their pyrolysis. Thepractical value of this latter feature of the invention will be readilyapparent when the possible difliculty of separating into their purecomponents mixtures of such isomeric esters, or mixtures of thecorresponding saturated glycols or diesters thereof, is considered.

It is preferred to employ in the process to which the invention relatesesters of the hereinbefore and hereinafter disclosedalpha,beta,omega-trihydroxyalkanes with saturated fatty acids, such asthe acetates, propionates, butyrates, valerates, caproates,oenanthoates, caprylates, pelargonates, caprates, and homologous esters,the formates being less desirable. There also may be employed in theprocess an ester of an alpha,beta,omega-trihydroxyalkane with anunsaturated fatty acid containing one, two, or even more non-aromaticcarbon-to-carbon multiple bonds, or esters wherein the acyloxy groupsare derived from aromatic carboxylic acids, such as benzoic acid, toluicacid, and n-butylbenzoic and xylic acids. In accordance with theinvention, the most favorable results in the matter' of yield of thedesired products and in the overall eflicacy of the process are obtainedwhen the triester that is employed is one which the acyloxy groups arederived from a saturated aliphatic monocarboxylic acid containing from 2to about 8 carbon atoms. The process is particularly effective whenthere are employed the triacetates of the above-defined trihydricalcohols.

In the execution of the process of the invention, the

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aforesaid triester of an alpha,beta,omega-trihydroxyalkane is heated toa temperature sufficiently elevated to effect the desired pyrolyticdecomposition, but not so high that undesired generalized decompositionof the organic materials that are present occurs. Temperatures of atleast 300 C. may be employed in accordance with the invention.Temperatures of at least about 350 C. preferably are employed.Considerably higher temperatures may be employed, if desired, up toabout 650 C. Within the indicated range of temperatures, the Optimumtemperature range depends inter alia upon the particular triester thatis employed in the process and upon the residence time of the triesterat the pyrolysis temperature. Lower residence times may be employed atthe higher temperatures, and, conversely, longer residence times may beemployed at the lower temperatures. When the pyof the invention isexecuted in a continuous manner, as"

by passing a stream of the triester into and through a reaction zoneheated to the desired reaction temperature, the residence time at thepyrolysis temperature is determined by the liquid hourly space velocity,which is the rate at which the triester, measured in the liquid state,is

passed into and through the reaction zone. In quantitative terms, theliquid hourly space velocity is equal to the volume of the triestermeasured in the liquid state, passed through a unit volume of thereaction space per hour. The liquid hourly space velocity that isemployed in the execution of the process of the invention may be variedwithin relatively wide limits, provided that under the existingconditions of temperature, presence or absence of catalysts, etc., it issuch that practicable conversions of the triester to the desiredproducts are obtained, without excessive generalized thermaldecomposition of the organic materials that are present. Generallyspeaking, liquid hourly space velocities within the range of fromabout.1 hr.- to about hr? will be found to be suitable. The optimum value, orrange of values, of the liquid hourly conditions under which the processis'exec'uted." ForeX- ample, at temperatures of from about 400 C. toabout 550; C. liquid hourly space velocities of from about .5 hrr' toabout 5 hrf frequently may be employedwith particular advantage. Atother temperatures, somewhat different liquid hourly space velocitiesmay be particularly advantageous.

Although the residence time'(or the liquid hourly space velocity in thecase of continuous operations); in conjunction with the pyrolysistemperature, may be employed as an expression of the severity ofthepyrolytic treatment, it isparticularly convenient; to define and tomeasure the 1 several conditions of the pyrolysis in terms of theproper! tion-of the initialamount of the triesterthat is-converted toothepproducts. We have found that particularly-ta vorableresults may beobtained in the practiceoftheprocess of the invention when the selectedconditions are such'that relatively highconve rsionszof theinitialtriester to other products are obtained. ,For' example,highly-far vorable results are obtained in the practiceof theinvention'when the conditions oi temper -ature residence time; and the;,l ile,;are'such that from about'SS 'to' about 85 of the tri esterisconverted to other products,- the balance being unchanged; Conditions'whichflead to lower total conversions, say down to about 10% of thetriester; may be employed, although in such cases the amount of thedesired products that "may be" obtained from 'a given amount of thetriesterper pass is correspondingly-less:

The process of the present'iuvention may be executed in either acontinuous, an intermittent, or a batchwise manner,;continuousjoperations beingmost efficacious.-- One"- particularlyefiective manner of operation comprises-pass ing a stream of the liquidtriester of the alpha-betapmegatrihydroxyallcene through a zone,-as anelongated reaction zone, that-is heated to the pyrolysis temperature, ata rate that is correlated with the temperature to provide'thedesiredpercentage conversion of the triester to other prod ucts. The reaction'Zonepreferably is defined by an elongated reaction tube which may beheated either internally or externally by suitable heating means. The"pyrolysis tube should be constructed of a suitable thermally and'chemically. resistant material, such asglass, nickel, stain-' lesssteel, Monel metal, or other resistant metals or'alloys of metals,quartz, porcelain, or the like. The pyrolysis tube'lrnay be otherwiseempty, or the tube maybe packed' I withinert or catalytically activesolids which favor the'de' siredpyrolyticdecompositions. Inert solidsservepri marily to assist transfer of heat tothe triesterand main,tenance of the temperature at the desiredvalue," and their presencethereby-may desirably increase the :overall etfec in the reaction tubeinclude, for example; glass, silica; iron;

stainless steel, silicon carbide; carbomlaluminumt oxide;-;-.

ceramic ,materials, e; g.,; porcelaimand "thetlikez The salts'such asacidiccalcium and/or silicon phosphates;

and the like, Because of theunexpectedlyhigh-yields "of? the desiredproducts that have been obtained in the herein'" described non-catalyticpyrolysis of the stated triesters; aii'da because of the possibilitythat-the presence ofcatalytic ally activemat'erials'may reduce theadvantageously high'yields the vapor state, e. g., in a continuousprocess, it may be desirable'to provide a'preheate'r o'r suitablevaporize'r'i'ro convert the liquid triester to the vapor state. 'Thevaporous ester may be diluted with an inert diluent gas, such asnitrogen, methane, or the like. Alternatively, the triester in theliquid state frequently maybe fed directly into the heated reaction zoneand its volatilization and pyrolysis efiecte'd simultaneously. If thereaction zoneis defined as by an elongated heated reaction tube throughwhich the triester'is passed, the intial portion of the'tube may serveas a preheater, or vapori'zen'the vaporous triester being subjected tofurther pyrolysis in the remaining portion of the reaction tube. Thepressure most conveniently-may be maintained at or about atmosphericpressure. However, the invention is not limited to the use ofatmospheric pressure, and pressures either above or'below atmosphericpressures may be employed if desirable.

The pyrolysis of carboxylic acid triesters of alpha,beta,-omega-trihydroxyalkanes containing at least four carbon I atomsin'accordance with the processof-the invention has beenfound toj'formproducts comprising principallydiesters=of unsaturated diols, whichdiols contain the samenumber" of carbon atoms as the .t'rihydroxyalkanefrom which the initial triesters were derived, accompanied by only minoramounts of products of other possible rea'ctions. In fact, the'onlyother products of pyrolysis which 1 have been detected have beenrelativelysmall amounts of 1 esters-of diolefinic monohydric alcoholswhich easily may be separated, as by fractional distillation, from theaforesaid esters of unsaturated diols. These esters of diolefinicmonohydric alcohols maybe recovered as useful products, or they may behydrogenated .to the corre-"" sponding 'saturatedmonoesters, which alsoare useful compounds.

The-mixture leaving the. pyrolysis zone comprises an 1amountwofthcarboxylic acid from which'the acyl groups tof the triestersubjected to pyrolysis were derived and-"one or'more diesters ofunsaturated diols asthe principal'produ'cts -ofthe pyrolysis. Thecarboxylic acid, whichprefe'rably is a' lower saturated aliphaticmonocar boxylic'acidt'may be removed or recovered from the mix'- ture'of'productsin any suitable manner; The entire mixii turez' thuS m-aybecooled to' about ordinary room temper-' aturesas by passing itthrough'a suitable heat exchanger tiveness of theprocess: Inert solidswhich may bezpresent' in heat exchange with. water, air, or othercoolant, and ii the carboxylic acid "thereafter "removed as bydistillation. Ari'otherconveni'ent method'of removing "the carboxylicacid by-productis tosubject the'mixture'as itleavesthe pyrolysis:zoneito-a stripping treatment, at a temperaturesuflicien'tly elevated tovolatilize-the carboxylic acidbut" not the esters'that are present.-Ofcourse,'other' methods of removing the carboxylicacid by productmay beem plo'yedy'if desired, as by'extractiomwith a selective solveh (e. g:"WBitCIgiiffllfi carb'oxylic acidiis water soluble) an'd .l the'like' Yarboxylicac'id diesters of the-unsaturated diols are desired as theultimate products, they may be recov xered fromi therproducts ofpyrolysis and purified as-by fractional-distillationoftheester-containiug portion of the by promoting other, undesiredreactions,.it'ispreferred' to executethe'proc'ess in the absence ofadded ca'talystsxx Inert substances, such as the inert solids referredto above;

are not regarded as catalysts.

The process of theinvention may be executed with the carboxylic acidester of the alpha,beta,omega trihy'droxy'- alkanein either the liquidphase or in' the-vapor. phases; When the operations are carriedoutiwiththe-.triesterfin...

.process'may be subjected' t'otheihydrogenation'treatmeht,-

reaction products; any'unconverted t'rie'sterof the alpha','--:beta,omega trihydroxyallcane also being separated at this": I timeifdesired; The unconve'rted triestermay berecycledthrough the pyrolysisstep oftheprocesses WithtreSh-feed in orderrto=increasekthe"overall3conversion of trie'st'e Whemth'e-processoftheinventionis directedferrediembodiin'ent'to the' preparation of esters vomegaidihydroxyalkanes, e.,: of alkylene' 'glyco'ls, coutainiug'atle'ast four" carbonatoms, the dies tersfof' un saturated diolswhichare'formedby the pyrolysis are liy drogenated byitreatment withmolecular hydrogen inthe presencerof 'a hydrogenationcatalyst tosaturate the-ole finic:b.onds 'that are'presentin the molecule. The'eh-tir mixture-"that isFproduced in the pyrolysisfstep' of thealthough-i preferably the carboxylic acicl -by produet offavored byfractionating the pyrolysis products only to such an extent thatsubstantial separation of the above stated fraction is achieved. Thefraction may contain varying amounts of possible side-products of thepyrolysis, depending upon the efficiency of the fractionation, thepresence of such side-products during the hydrogenation treatment notbeing detrimental.

The hydrogenation of the fraction comprising essentially .the carboxylicacid diesters of the unsaturated diols may be effected by. subjectingthe fraction to the action of molecular hydrogen in the presence of ahydrogenation catalyst under conditions which favor the reduction ofolefinic bonds to saturated carbon-to-carbon bonds. As the hydrogenationcatalyst there may be employed any of the metals, or compounds ofmetals, or mixtures thereof, customarily referred to in the art andemployed as hydrogenation catalysts. Suitable metals which may beemployed as the hydrogenation catalyst include, for example, Ni, V, Pd,Pt, Cu, Cr, Fe, Co, Ru, Mo, W, Ir, Ru, Ag, and suitable compoundsthereof, such as oxides and sulfides thereof. It is preferred to employthe base metal hydrogenation catalysts because they have been found .tohave a desirably high degree of efiicacy and because they am easily andeconomically prepared. Nickel catalysts, such as .the Well-knowncatalyst referred to in the art as Raney nickel catalysts, areparticularly desirable. In place of the Raney nickel catalyst, there maybe employed nickel catalysts that have been prepared, for example, by.thermal decomposition of suitable compounds of nickel, by mechanicalsubdivision of massive nickel, by

. electrodeposition, or according :to other known methods.

Catalytically active compounds of metals which may be employed as thehydrogenation catalyst include, among others, copper chromite, copperoxide, molybdenum oxide,

'mixtures of oxides of copper and of molybdenum, tungsten sulfide, andtungsten-nickel sulfide. The catalyst may be employed in the finelydivided state and suspended in .the fraction to be hydrogenated, or itmay be carried on "an inert or catalytical-ly active supportingmaterial, such as' carbon, pumice, silica, clay, alumina, ktieselguhr,or the like.

In the hydrogenation step of the process of the invention, thecarboxylic acid esters of the unsaturated diols are subjected to theaction of the molecular hydrogen at an elevated temperature and undersuperatmospheric pressures of hydrogen in the presence of thehydrogenation catalyst. Amounts of the catalyst from about 1% to about20% by weight of the fraction that is to be hydrogenated are generallysatisfactory, although either 300 C. may be employed during thehydrogenation treatment, a preferred range being from about 50 C. toabout 150 C. Hydrogen pressures of from about 250 pounds per square inchupwards are suitable. There is no known upper limit to the pressures ofhydrogen that may be employed, although for practical reasons :it-rarelyis desirable or necessary to employ hydrogen ipressures' above-about10,000 pounds per square inch.

vents, and the like.

A preferred range of hydrogen pressures is from about 500 pounds persquare inch to about 5000 poundsper square inch. f

The carboxylic acid diesters of unsaturated diols that are produced bythe pyrolysis step of the process, or a fraction of the pyrolysisproducts comprising the same, may be hydrogenated by exposing them tothe action of hydrogen gas under the aforesaid conditions of temperatureand pressure of hydrogen gas in the presence of the hydrogenationcatalyst until absorption of hydrogen is essentially complete. It hasbeen discovered that the theoretically calculated amounts of hydrogenbased on the degree of unsaturation of the fraction that is to behydrogenated, may be absorbed. The absorption of hydrogen may bedetermined by measuring in any suitable known manner the amount ofhydrogen that is absorbed. Alternatively, the hydrogenation may becontinued until absorption of hydrogen ceases. The hydrogenationtreatment ofthe invention may be carried out in either a continuous, anintermittent, or a batchwise manner. Any suitable apparatus of thecharacter customarily employed for hydrogenation reactions may beemployed.

The hydrogenation step of the process of the invention may be effectedin the presence or absence of a suitable solvent, such as an inertorganic solvent. Suitable organic solvents include, for example,saturated hydrocarbon solvents, ethers, esters,'alcohols, aromatichydrocarbon solvents, halogen-containing hydrocarbon sol- When a solventis employed it may be used in an amount ranging up to.90% by weight ormore of the reaction mixture. The carboxylic acid diesters ofunsaturated glycols that are produced by the pyrolysis step of theprocess thus can be effectively hydrogenated in the form of a 10% to 40%by weight solution in a saturated hydrocarbon or other suitable solvent.However, the presence of an inert solvent during the hydrogenationtreatment is not a prerequisite to its successful practice, and,thereof, the invention also includes such hydrogenation when no solventis. adde to the reaction mixture. 1

After completion of the hydrogenation step of the process, the desiredcarboxylic acid diester of the alpha, omega-alkanediol may be recoveredfrom the mixture in any suitable manner. The catalyst, if suspended inthe mixture, may be removed by filtration, centrifuga tion, or inequivalent ways. The solvent, if one is present, may be removed byevaporation, distillation, or the like, and the products of thehydrogenation thereafter separated in any effective manner, fractionaldistillation, as under reduced pressure, being preferred. It was a quiteunexpected result of the present process-that the principal, andfrequently the only diester present in appreciable quantities, is thecarboxylic ester of the alpha,omega-dihydroxyalkane containing the samenumber of carbon atoms in the molecule (exclusive of the acyloxy groups)as the triester that was subjected to the pyrolysis. No significantquantities of the possible isomeric esters of beta,omegaand/oralpha,beta-dihydroxyalkanes have been found. There may be present, inminor amounts that may be influenced by the efliciency of thefractionation of the products of the pyrolysis step of the process, thecorresponding carboxylic acid alkyl ester, presumably formed bysaturation of the aforementioned esters of diolefinic monohydricalcohols. Since these products ordinarily have substantially differentboiling points, they may be easily separated during purification of thehydrogenation products.

The process of the invention is particularly valuable for thepreparation of carboxylic acid diesters of 1,6- hexanediol, fromcarboxylic acid triesters of 1,2,6-hexanetriol, the lower saturatedaliphatic monocarboxylic acid esters preferably being employed. When atriester of 1,2,6-hexanetriol, e. g., the triacetate, is subjected topyrolysis in accordance with the process of the invention, the principalproduct has been found to be a com- 7 plei mixture oresters ofi (3smono-olefinic' diols with the *carbox ylici' acid,- possibly: with very:minor amounts of esters of Ca diolefinic monohydric alcohols.-There'also is'ronae'd the-carboxylic' acid from which 'the'acy'l groups"of'the triester'were derived. There-alsomaybe-present varyin'g''amonnts of unreacted 1-,2,6-hexanetriol 'trie'ster. In thec'ase'"ofthei lower saturated aliphatic mono'carbox ylic acid'e'sters of1,2;6-hexan'etriol the pyrolysis-may be' -efie'c'tedadvantageously atfromabout *350"- (2. to about 500" C. and at a 'resid'ence time orliquid h ourly spac'e'velocity of from about 0.5 to about 2.5 hr.

The rhixture produced by the pyrolysis may be separated by"fractional'distillation so as to recover a-fractioriihavi'ng an increased contentof"-the diesters 'of Ca fr-loin) oletinic dihydric=alcohols; and also ifdesired to I about 110 C.'under 3 mm.-Hg pressure, or overan*equivalent'temperature range under'other pressures, may be separatedas'the fraction'rich in hexenylenediacetates. Of course,the esters ofother carboxylic' acids may distill oVer a'SOmeWhat 'ditferent range oftemperatures.

"The fraction-rich in hexenylene diesters may. be hydro- :genated underhydrogenation conditions which have been refer'-red" to hereinbefore,to-saturate the olefinicbonds. "'After' completion of thehydro'genation,- -any -minor amounts of other products may be separated'frorn the :die'ster of l,6 hexanediol that is formed as the principalproduct, as by fractional distillation of the products of hydrogenation;If the free hexamethylene glycol rather th'anits' diester is desired asthe ultimate product, the ester may be saponified according many of themethods that are known in the art to obtain the desired glycol.

When"reference-is made'herein to alpha, beta, omegat1ihydroXy-alkanescontaining at least four carbon atoms, and-totheiresters, it is intendedto refer to those saturated aliphatic triols which'cont'ain two primaryalcoholic -hy droxyl g'rotips'anda third alcoholic hydroxyl group allbonded to separatecarbon atomsin a chain of at least "fourcarbonatoms,two of the 'hydroxyl' groups being attached to adjacent carbon atoms.Regarding the vicinal -hydroxyl groups' as attached to the'alpha andthebeta carbon atoms; the second terminalhydroxyl group, -i. e., theone' at the terminal, or the omega; carbon atom, may be separated fromthe beta carbon atom' by two or more carbon atoms. We preferably-employtriestersof alpha, -betapmega trihydroxyalkanes in which th'eomegacarbon 1 atom-is separated-from thebeta carbon atom by not more "that'about 5 atoms of 'carbon. T he carbonatoms in this smear-grou er fourormorecarbon atoms may be unst'ibstituted,- or'they' may be'substitutedby one or'more groups. It is'preferred toernploy esters of alpha,-betaomega trihydroxyalkanes "which contain -not over l out 16carbo'n'atom's', e'ir'clusiye of the'carbo'n atoms in the acyl groups.

Representative alpha, beta,omega-trihydroxyalkanes, carboxylic acidesters of which may be converted by the process of the invention toesters of alphapmega tlihydroxyalkanes include in addition to1,2,6'hexanetriol, -l ,'2 ;4-butanetriol, l-,2,5-pentane'triol, andcarboxylic acid esters of analogous and homologous;alpha,beta,omegatrihy'droxyalkanes. Generally: speaking; the esters of-alpha;beta,omega trihydroxyalkanes1 which we mayemploy inithe processor the invention-have structuresnac- --cording--to the-formula V-Robo-onz-(onon on onrooon irrwhich n represents an integral number,preferablyone not=greater than 5, and R represents a monovalenthydro---carbon group containing up to 18 carbon atoms, preter- -ablyan alkylgroup, such as a loweralkyl group. We also may employ esters ofalpha,beta,omega-trihydroxyalkanescorres'ponding to theabove formulawhen one or -m01e of the hydrogen atoms in the: formula have been:replaced by an alkyl group, preferably a lower 'tilkyl group, such ascorresponding esters-of 2,5-dimethyl-1-,2 ,6- hexanetriol, lZ-methyl-1,2,6-heXanetriol, 2,5-diisobutyl- -1;2,6-hexanetriol,2,4-dimethyl-1,2,5 pentanetriol, and the like, the preferredcsters ofsuch: alkyl-substituted alpha,beta,omega-trihydroxyalkanes' being the:esters .of such al'pha,beta,omega trihydroxyalkanes having not 1 morethan two alkyl substituentgroups 1 replacing hydrogen atoms in theforegoing formula. -'From thettriesters of the unsubstitutedalpha,beta,omcga-trihydroxyalkanes and'l'ower aliphatic monocarboxylicacids containing at 'least four-carbon atoms there areobtainedconesponding estersof alpha,omega-dihydroxyalkanes with t1oweraliphatit:mono'carboxylic acids containing at :least "four carbon-atoms.These products correspond to :the struc- RCOO-CH2'--( CH2)i1'-CH2CH2OOCR in which t re resents an integral number not g'reatefthan5 "and RCOOrepr'esents theac'yloxy group of La'l'o'wer'aliphatic"mo'nocarb'oxylic acid containing at'leastffour carbon atoms.Illustrative ofthese'are 1,6 hexanediol -dibutyrate, l,5-penta'nedioldicapr'ylate, and l,5 -pent anediol'dicaproate. From 'este'rsofalkyl-substituted alpha,-

' beta,omega?trihydroxyalkanes there are, obtained ia'ccordin'g"to"thepr'ocess of'the invention esters of'branch'ed' chain alpha,omega-glycolshaving structures corresponding to the formula RCOOCH2'(CH2)1z-CH2'CH2OOC in'which n represents an integral number not "greater than5 and RCOO represents the acyloxy group of an acid selected'from 'thegroup consisting of lower'aliphatic, monoca'rboxylic acids and aromaticmonocarb'oxylic acids, wherein a hydrogen atomon a beta carbon'atom 'isrepla'cedby a lower alkyl' group and from nonetoone,

inclusive, hydrogen atom on a different "non-terminal carbon atom of thelinear carbon chain isireplacediby'a' 'dim'ethyl-l',6 '-hexanedioldib'u'tyrate. The novel esters are useful 'i'nter'aliaas plasticizersfor polyvinyl chloride. 1-.

' The followinge'xample's' will :illustrate some ;of the possible secifie'embodiments of the, invention. 'lt'will'lbe understood that 'theexamples are intended only 'tobe illustrative of the invention that isdefined more broadly in the appended claims. In the examples, thepartsare "by weight.

ExampIe I A vertically {positioned cylindrical reaction?tribee'onst'ructed of nickeland having a diameter 015L625 inch 'afidalength of 42 inches, was filled with S to 14 inesh silicon carbidechips. The top of the tube was"closed*from" the atmosphere and wasprovided with an inlet through which liquid feed'could be'supplie'd inmeasured quantities. The

; lowerend of the tube was connected through a short watenjacketedcondenser to a suitable --receiving: flask for :efiiuent from: thereaction tube The reaction tubeftwss surrounded: by :-'::thehndstaaea11yontm1lect e'lectl ieal heater's which were regulated with the aid of athermocouple placed in the interior of the reaction tube.

The reaction tube and its contents were heated to 450 C. Liquid1,2,6-hexanetriol triacetate then was fed into the top of the reactiontube onto the heated silicon carbide chips at a liquid hourly spacevelocity of 1.47 hrr' the velocity being calculated on the basis of thefree space in the packed tube. The liquid product issued from the vbottom of the tube and was collected in the receiving flask.

When 215 parts of 1,2,6-hexanetriol triacetate had been 'fed to thepyrolysis tube, 200 parts of liquid products had collected in thereceiving flask. The liquid crude product thus obtained was fractionallydistilled under reduced pressure. A fraction distilling from 56.5 C to62.2 C. under 100 mm. Hg pressure was collected and found to be composedprimarily of acetic acid. After distillation of a second fraction,distilling from 42 C. to 89 C. under 3 mm. Hg pressure, there wascollected a fraction distilling from 89 C. under 3 mm. Hg pressure to115 C. under less than 1 mm. Hg pressure, amounting to 81 parts andconsisting predominantly of diacetates of nonvinylic hexenediols.Fifty-one parts of unreacted 1,2,6- hexanetriol triacetate wereseparated as a fraction distilling at 115 C. to 116 C. under less than 1mm. Hg pressure. Seven parts of residue remained in the still kettle.

A solution of 22 parts of the fraction consisting predominantly ofhexenediol diacetates dissolved in 78 parts of isooctane was placed in ahydrogenation bomb with 2 parts of Raney nickel hydrogenation catalyst.The mixture was subjected at 100 C. to the action of hydrogen gas undera pressure of 1400 pounds per square inch until hydrogen absorptionceased. The catalyst was removed by filtration and the filtrate wasdistilled. There were recovered 14.9 parts of hexamethylene glycoldiacetate disstilling at 103.5 C. to 106 C. under 3 mm. Hg pressure.

The hexamethylene glycol diacetate was dissolved in 30 parts ofanhydrous methanol containing 0.25 part of sodium, and methylalcohol-methyl acetate azeotrope was distilled from the mixture untilthe theoretically calculated amount of methyl acetate was removed. Thealkali was removed by passing carbon dioxide into the residual solutionand filtering off the precipitate. The filtrate was dis tilled, withcollection of 7 parts of hexamethylene glycol at 110 C. to 122 C. under4 mm. Hg pressure. The hexamethylene glycol melted at 36 C. to 38 C.both alone and when mixed with a sample of glycol prepared by anothermethod and melting at the same temperature.

Example II The tripropionate of 1,2,6-hexanetriol is pyrolyzed accordingto the method of the preceding example. The resulting mixed liquidproducts are fractionally distilled and a fraction comprisingpredominantly dipropionates of non-vinylic hexenediols is collectedseparately. This fraction is dissolved in about twice its weight ofisooctane. The resulting solution is hydrogenated over copper chromiteby treatment with gaseous hydrogen under a pressure of about 2000 poundsper square inch at a temperature of about 150 C. until absorption ofhydrogen ceases. After separation of the catalyst the resulting solutionis fractionated by distillation under reduced pressure, the fractioncomprising the dipropionate of hexamethylene glycol being collectedseparately. The dipropionate of hexamethylene glycol distills at about106 C. under 2 mm. Hg pressure.

Example III A fraction consisting predominantly of diacetates of'nonvinylic hexenediols, prepared as in Example I, is hydrogenated inthe form of a 25% by weight solution in isooctane in the presence ofcopper chromite and under a .hydrogen pressure of about 2000 pounds persquare inch .and at about 150 C. The diacetate of hexamethylene glycolis recovered from the products of the hydrogeiia tion according to theprocedure illustrated in Example I.

Example IV Forty-one parts of 2,5-dimethyl-1,2,6-hexanetriol"areacetylated by treatment with acetic anhydride in the presence of aceticacid and after standing over night themixture is rapidly distilled torecover the acetate estei. Tlie drogenation of this mixture over Raneynickel catalyst at 7 about C. under about 1200 pounds per square inchhydrogen pressure and fractionally distilling the products of thehydrogenation.

2,5dimethyl-1,2,6-hexanetriol used in this example can be prepared from2,5-dimethyl-3,4-dihydro-1,2-pyran-2- 3 carboxaldehyde by hydrogenationat C. to C.

in aqueous ethanol or other aqueous solvent in the presence of acid anda hydrogenation catalyst, such as Raney nickel catalyst.

This application is a continuation-in-part of copending applicationSerial No. 207,865, filed January 25, 1951 now abandoned, which in turnwas filed as a continuationin-part of application Serial No. 769,066,filed August 16, 1947, now abandoned.

We claim as our invention:

vinylic 1,6-hexenediols, which comprises pyrolyzing by heating at atemperature within the range of from about 300 C. to about 65 0 C. thetriacetate of 1,2,6-hexanetriol and recovering from the products of thepyrolysis a dirange of from about 300 C. to about 650 C., a lower fattyacid triester of 1,2,6-hexanetriol and recovering from the products ofthe pyrolysis a lower fatty acid diester of a non-vinylic1,6-hexenediol.

3. A process for the preparation of lower fatty acid diesters ofnon-vinylic 1,6-hexenediols, which comprises passing a lower fatty acidtriester of 1,2,6-hexanetriol through a plyrolysis zone heated to withinthe range of from about 400 C. to about 550 C. at a liquid hourly spacevelocity of from about .5 hr." to about 5 hr.- whereby said triester ispyrolyzed to the lower fatty acid and lower fatty acid diesters ofnon-vinylic 1,6-hexenediols.

4. A process for the preparation of diacetates of nonvinylicalpha,omega-alkenediols, which comprises pyrolyzing by heating withinthe range of from about 300 C. to about 650 C. a triester having theformula in which n represents an integral number not greater than 5.

5. A process for the preparation of monocarboxylic acid diesters ofnon-vinylic alpha,omega-alkenediols, which comprises pyrolyzing byheating within the range of from about 300 C. to about 650 C. a triesterhaving the formula 0 O C R RC 0 O-CHr-(OHz) n-OH-CHz-O O C R in whicheach RCOO represents the acyloxy group of a lower fatty acid and nrepresents an integral number not greater than 5.

6. A process for the production of a monocarboxylic acid diester ofhexamethylene glycol, which comprises pyrolyzing by heating within therange of from about 300 C. to about 650 C. a lower fatty acid triesterof 1. A process for the preparation of diacetates of nonv a ran eatmospheric pressure an at an elevated temperature in the presence of ahydrogenation" -catalyst to produce a lower iatty acid ;di esten rothexamethylene glycol, a

7.7.- A. process; r fiOIrf the. production ..of 1monocarboxylici id fiestfi al m t en sel whish sm se py q i h tins w n n esq IQmb 300 rcflto'aoouts650? C'. analkanetriol triestershaying,

inssvh ijchtelach ,RCOQ; represents. the; acylogry, group of a,

logy tiattyacid land In representsanflintegral' number 'notomega-alkanediols and hydrogenating thespyrolysis .prod1 uctrbyactionthereon of molecular hydrogen Zunder'. supep,

atmosphericpressurerandsat elevated temperatures in the 7 .20carboxylic, acid, diester of'the' polymethylene fglycoljhav r preser'lce'bfr a hydrogenationrcatalyst to produce .a mono:

ing jth'efs'arne number. of carbon atoms as' saidualkanetriol. i

SWA process for theprcparation of a monocarbbxylic acid di'ester of apolymethylene glycol, which comprises hydrogenating in the presence of ahydrogenation cata-Q lyst .at a temperature and u'nder a pressure-ofhydrogen conducive to hydrogenating reactions va product'pro ducedv 9: Aprocess for the preparation of *a' monocarboxylicg'j acid -diester of'liexamethylene glycol which comprises hyclrogen-ating in the presence ofa hydrogenation catalyst" aka-temperature within the ran'ge-of fromabout '40" C." to "aboutBOO" C." 'an'd'under' a pressure of hydrogen of12 Q-abQ F -PP fl 'WI qua n h. t tbels 9,0 PoundS Pas u e n h m re r d bP r l attemperatures: withinthe range of from about 300i.

toab outjojfi" C. of a fatty-acid trie ster-of a 1-,2 ,6-h exane- Vtriol and comprisingnatleastmone-rfatty:acid diesterot a;

non-vinylic l ,6 -hexenediol..

10.7 A process for the preparation of amonocarboxylic, acid diester. .of.a non-yinylic: alpha,ornega-alkenediol,s

which comprises 5 :pyrolyz ing a triester selected from vthe. groupconsisting of (a) triesters of trihydroxyalkanesw in which eachRrepresents a; hydrocarbon group rcontaine ing' up to 18 carbon atoms andn represents an integral number not, greater vthanS, and] (b)i'fth osealkyl-s ubjstii I tuted triesters ofalphagbeta',omegadrihydroiiyalkanes,

whichralkyl-substituted triesters arereprefsented by then:

foregoing formula When/the hydrogen atom on the fb eta w carbon atom isreplaced by ar lower alkyl vgro'u p and j.

from none to one, inclusive,-hydro'gen atom on a difi ent non-terminalcarbon-atom of the 'linean'carbo n?chain} ofvthe residue of theunsubstituted alphaibeta-dmega trihydroxyalkane is replaced tbya loweralkylg'roup as the only additional 'substituent and R and n' aredefinedas hereinbefore; i

References-Cited'in the -file' of' this'patent UNITEDWSTATESOPATENTS2,122,812 21 GrolL et aL; \,Ju1y;5, 1938:: 2,251,983', Chitwood Aug'.12,;194'l i 2,700,656. Emerson etal ;.Jan'.s.,25, 1955 OTHER REFERENCESFrankei CA 3 0,,1740 ,(1936) Goldfarbd CAQ33, 4599x1939 Schnieppet-'al.: J. A..C. S; 67, 5456j(19 ).4 Bried et 211.: .Ind. EngnChemL39f, 484,9.l (..1947). Linduska et alJChem. Abst...41(19 .47,) 3580/2;

Wagner and 200k: Synthetic .Or g anic.,Chem. .Wiley

10. A PROCESS FOR THE PREPARATION OF A MONOCARBOXYLIC ACID DIESTER OF ANON-VINYLIC ALPHA,OMEGA-ALKENEDIOL, WHICH COMPRISES PYROLYZING ATRIESTER SELECTED FROM THE GROUP CONSISTING OF (A) TRIESTERS OFTRIHYDROXYALKANES HAVING THE FORMULA